1. Field of Invention
The present invention relates to a multiple flexible wiring board in which a plurality of flexible wiring boards having bendability are arranged dispersed, a method for producing that multiple flexible wiring board, a method for producing a flexible wiring board, and that flexible wiring board.
2. Related Art
A multiple flexible wiring board, a method for producing that multiple flexible wiring board, and a flexible wiring board according to a conventional example will be described with reference to FIGS. 14 to 17.
FIG. 14 is an exploded perspective view of a multiple flexible wiring board according to a conventional example. FIG. 15 is a plan view of the multiple flexible wiring board according to the conventional example. FIGS. 16(A) and 16(B) are cross-sectional diagrams that show the broken cross-section at arrow XVI in FIG. 15. FIG. 16(A) shows a layered state in a temporary fastening step prior to thermocompression bonding, and FIG. 16(B) shows a layered state after thermocompression bonding with a pressure bonding step. FIGS. 17(A) to 17(C) are explanatory diagrams that explain a flexible wiring board according to the conventional example. FIG. 17(A) is a plan view, FIG. 17(B) is a side view, and FIG. 17(C) is a side view that shows a state of use.
A multiple flexible wiring board 101 is configured by layering, in this arrangement, a first wiring base material 112, a first covering film layer 113 that covers one face of the first wiring base material 112, an adhesive sheet 120 that bonds the first wiring base material 112 and a second wiring base material 116 to each other in a layered state such that they face the first covering film layer 113 and a second covering film layer 117, the second covering film layer 117 that covers one face of the second wiring base material 116, and the second wiring base material 116.
The first wiring base material 112, the first covering film layer 113, the adhesive sheet 20, the second covering film layer 17, and the second wiring base material 16 are temporarily fastened in an aligned and layered state (a temporary fastening step), and with thermocompression bonding that applies heat and pressure from both faces of the first wiring base material 12 and the second wiring base material 16, the first wiring base material 112 and the second wiring base material 116 are bonded with interposition of the adhesive sheet 120 (a pressure bonding step).
The first wiring base material 112 and the second wiring base material 116 each have an insulation layer and a conductor pattern (not shown), and have flexible wiring board corresponding portions 112d and flexible wiring board corresponding portions 116d as areas that correspond to separate flexible wiring boards 111. The insulation layer of the first wiring base material 112 and the second wiring base material 116 has flexibility, and the conductor pattern is formed appropriately on one face or both faces of the insulation layer.
A plurality of the flexible wiring board corresponding portions 112d and the flexible wiring board corresponding portions 116d are formed and arranged on the multiple flexible wiring board 101, and it is possible to form a large number of flexible wiring boards 111 in a single processing step. Here, a state is shown in which by arranging the flexible wiring board corresponding portions 112d (the flexible wiring board corresponding portions 116d) in a plane such that they are symmetrically opposed, the area usage ratio is improved, and by further arranging the flexible wiring board corresponding portions 112d (the flexible wiring board corresponding portions 116d) in four rows, a total of eight flexible wiring boards 11 are formed together.
In the adhesive sheet 120, an opening portion 121 (for the convenience of this description, the opening portion prior to thermocompression bonding may be indicated as an opening portion 121a, and the opening portion after thermocompression bonding may be indicated as an opening portion 121b) is formed in order to form a hollow portion 111s after layering. Excess adhesive of the adhesive sheet 120 is melted due to the application of heat and pressure by the thermocompression bonding step and flows into the opening portion 121, forming an adhesive outflow portion 120f. Accordingly, the opening portion 121b is influenced by the adhesive outflow portion 120f and thus is smaller than the opening portion 121a. 
After thermocompression bonding, the multiple flexible wiring board 101 is separated (a separation step) by pressing (cut-shaping) with a metal die of a predetermined shape that corresponds to the flexible wiring boards 111, thus forming a plurality of the flexible wiring boards 111 at the same time.
However, with respect to the separate flexible wiring boards 111, the adhesive outflow portion 120f may be formed in the hollow portion 111s, and a completely hollow state does not occur, so sometimes it is not possible to surely maintain flexibility. For example, a usage state in which those portions have been bent is shown in FIG. 17(C), but in some cases they will not be bent with a smooth curve as shown, or damaged. That is, there is the problem of having a serious effect on bendability, and in some cases the flexible wiring boards 111 will have low reliability.
In order to address such problems, it has been proposed to semi-harden the adhesive sheet 120 in advance, and furthermore adjust conditions such as the temperature and pressure when thermocompression bonding, and the melt viscosity of the adhesive (for example, see JP H6-283849A). However, with this method, it is difficult to set conditions, so adjustment is difficult, and thus solving the problems is difficult.